Powdered or other particulate, curable phenol-aldehyde based resins, e.g., phenol-formaldehyde (PF) resins, have found wide use as an adhesive for a variety of lignocellulose composite products such as oriented strand board (OSB) and other similar wafer or chip board products. PF resins are typically prepared by reacting a molar excess of formaldehyde with phenol under liquid, e.g., aqueous, alkaline reaction conditions. The resulting liquid PF resin is then spray-dried to produce the curable PF resin powder that is used as an adhesive. One drawback to the use of PF resins as an adhesive is that PF resins are petroleum derived compounds and thus subject to variations in price and limitations in production quantities. There is also an interest in reducing the amount of formaldehyde, both during the production of PF resins and in finished lignocellulose composite products.
One approach to reducing the amount of phenol and formaldehyde in PF resins has been to use lignin as a reactant in the preparation of aldehyde-based resins. Lignin is a wood-derived polyphenol polymer that is most commonly produced as a by-product from the kraft wood pulping process. Typically, “black liquor” obtained from the kraft process is separated from the remaining wood pulp and then lignin is isolated from the black liquor by any number of methods. These new chemical species are commonly prepared by reacting lignin with the PF resin and/or an aldehyde/phenol starting material to form a new lignin modified aldehyde-based resin. Such lignin modified aldehyde based resins, however, are not only expensive, but also are complex and time consuming to make.
There is a need therefore, for improved phenol-aldehyde based adhesives for making lignocellulose composite products that can include a reduced amount of phenol and/or aldehyde.